The present disclosure relates to an organic electroluminescence (EL) display unit displaying an image with use of an organic EL effect, a method of manufacturing the same, and a color filter substrate used in such an organic EL display unit.
In recent years, as alternative to a liquid crystal display unit, attention is given to an organic electroluminescence display unit (hereinafter simply referred to as “organic EL display unit”) using an organic electroluminescence device (hereinafter simply referred to as “organic EL device”). The organic EL display unit is of a self-luminous type, and has low power consumption. Moreover, since the organic EL display unit has a wide viewing angle, superior contrast, and sufficient responsivity with respect to high-definition high-speed video signals, the organic EL display unit has been actively developed and commercialized for practical use as a next-generation flat display unit. In particular, research on an active matrix (AM) type organic EL display unit including a thin film transistor (TFT) for light emission control in each pixel has been actively conducted.
In the case where such an active matrix type organic EL display unit is of a bottom emission type in which the TFT is disposed below an organic EL device and light is extracted from a bottom of the organic EL device, light passes only through a portion where the TFT is not disposed to exit from the organic EL display unit. Accordingly, an aperture ratio easily declines. On the other hand, in a top emission type organic EL display unit in which light is extracted from a top of the organic EL device, a decline in aperture ratio is suppressed; however, a transparent conductive film is used for an upper electrode (a counter electrode). Since the upper electrode is formed to have a thin thickness, the upper electrode has high resistance, thereby causing an IR drop (a voltage drop).
The IR drop is caused by the following reason. Although electrons or holes are supplied to each pixel through the upper electrode, a typical upper electrode is formed as a common electrode for respective pixels, and a feeding point to the upper electrode is provided only at an end of a substrate. Therefore, when a transparent conductive film having higher resistance than a current supply line to a lower electrode is used for the upper electrode, variations in wiring resistance according to a distance from the feeding point to each pixel are not negligible. Accordingly, when the distance between the feeding point and the pixel is increased, a drop in effective voltage applied to the organic EL device of each pixel is considerable, and variations in in-plane luminance are pronounced.
Therefore, there is proposed a technique of suppressing a drop in effective voltage through disposing an auxiliary power supply line made of a low-resistance material in a drive substrate where TFTs are disposed, and electrically connecting the auxiliary power supply line to an upper electrode to supply a current with use of the auxiliary power supply line (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-230086). However, in this technique, it is necessary to avoid adhesion of an organic substance onto the auxiliary power supply line, and when an organic layer is formed of a low-molecular material by, for example, an evaporation method, a precisely processed evaporation mask covering an auxiliary electrode is necessary. A typical evaporation mask is formed by etching of a metal sheet with a thickness of approximately 10 □m to 100 □m or by electroforming. Even if any of these processing methods is used, it is difficult to form an evaporation mask with higher definition, and in particular, it is difficult to form an evaporation mask for a large-scale product. In addition, in the case where the precisely processed evaporation mask is used, it is necessary for the evaporation mask to be precisely aligned for evaporation. Since an increase in temperature is caused by radiant heat from an evaporation source during evaporation, misalignment or the like is easily caused by a difference in heat expansion coefficient between the evaporation mask and a substrate. It is difficult for such a technique to address an increase in size or definition of a panel.
On the other hand, when a configuration in which a common light-emitting layer (for example, white or blue) is provided for all pixels is adopted, it is not necessary to color-code light-emitting layers of pixels; therefore, a sufficiently large opening width is obtained, and the above-described precise processing of the evaporation mask is not necessary. Therefore, it is easy to cope with an increase in size or definition of the panel. However, power feeding to the upper electrode is possible only at the end of the substrate; therefore, variations in light emission luminance caused by the above-described IR drop are inevitable.
Therefore, there is proposed a top emission type organic EL display unit with a configuration in which an auxiliary electrode electrically connected to the upper electrode is included in a counter substrate (for example, refer to Japanese Unexamined Patent Application Publication No. 2011-103205).